The present invention relates to a piezoelectric/electrostrictive device having a movable portion which operates on the basis of displacement of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device which can detect displacement of a movable portion by a piezoelectric/electrostrictive element, and particularly relates to a piezoelectric/electrostrictive device which is excellent in strength, impact resistance, and moisture resistance and has a high amplitude efficiency and can largely operate the movable portion.
Recently, in the fields of optical and magnetic recording, precision-machining or the like, a displacement element which can adjust an optical path length or a position in sub-micron precision has been required, and the development of a displacement element which uses displacement based on the inverse piezoelectric effect or electrostrictive effect caused when voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric substance) has been progressed.
For example, as shown in FIG. 2, a piezoelectric actuator 21 is disclosed in Japanese Patent Laid-Open No. 10-136665, in which a fixed portion 25, a movable portion 24, and a beam portion 26 for connecting these portions are unitarily formed by providing a hole portion 28 in a plate-like substance made of a piezoelectric/electrostrictive material and further, an electrode layer 22 is provided to the beam portion 26.
In the actuator 21, when voltage is applied to the electrode layer 22, the beam portion 26 expands and contracts in the direction of connecting the fixed portion 25 and the movable portion 24 by the inverse piezoelectric effect or electrostrictive effect, and therefore, it is possible to displace the movable portion 24 by arc-like displacement or rotary displacement in the plane of the plate-like substance.
However, in the actuator 21, since displacement in the expanding and contracting direction of a piezoelectric/electrostrictive material (that is, in the direction in the plane of the plate-like substance) is transmitted to the movable portion as it is, displacement of the movable portion 24 is rather small.
Furthermore, in the actuator 21, since all parts are constituted by a piezoelectric/electrostrictive material which is a brittle and relatively heavy material, there has been a problem in that the actuator 21 itself is heavy and it may easily be affected by a harmful vibration in operation (for example, a residual vibration or a noise vibration in high speed operation). In addition, the material has low mechanical strength and is inferior in handling efficiency, impact resistance, and moisture resistance.
In the actuator 21, in order to solve the above problems, it has been proposed to fill the hole portion 28 with a filler having flexibility, but it is clear that the efficiency of displacement based on the inverse piezoelectric effect or electrostrictive effect is lowered in the case of using fillers.
The present invention is made due to such problems of the prior art, and it is an object thereof to provide a displacement element in which a movable portion can largely be operated and is not affected by a harmful vibration in operation, and, additionally, has excellent mechanical strength, handling efficiency, impact resistance, and moisture resistance. As a result, the sensor element can detect a vibration of the movable portion accurately.
In the present invention, there is provided a piezoelectric/electrostrictive device comprising:
a driving portion which is driven by displacement of a piezoelectric/electrostrictive element;
a movable portion which operates on the basis of a drive of the driving portion; and
a fixed portion for supporting said driving portion and movable portion,
wherein the device has a driving portion including thin plates facing each other and a thin film piezoelectric/electrostrictive element formed on a surface of at least one of the thin plates and said fixed portion and said movable portion are connected by the driving portion.
As a specific mode of a piezoelectric/electrostrictive device of the present invention, a device can be cited, in which a movable portion and a fixed portion are shaped like a rectangular parallelepiped and thin plates facing each other are spanned so that the sides of the above movable portion and the above fixed portion are continuous.
The piezoelectric/electrostrictive device of the present invention is a device in which a driving portion is driven in the direction perpendicular to the direction of displacement of a piezoelectric/electrostrictive element and a movable portion operates in the plane including the driving direction of the driving portion. Furthermore, it is also possible to use the driving portion for detection of displacement of the movable portion.
Moreover, the piezoelectric/electrostrictive device of the present invention is preferably a device having at least two driving portions, and it is preferably a device in which the width of a thin plate is 5 or more times the thickness of the thin plate.
As a piezoelectric/electrostrictive element constituting a piezoelectric/electrostrictive device of the present invention, it is preferable to use a layered type piezoelectric/electrostrictive element in which a lower electrode, a piezoelectric/electrostrictive film, and an upper electrode are laminated, or a piezoelectric/electrostrictive element which comprises a piezoelectric/electrostrictive film, and a first electrode and a second electrode having a comb-like structure and has a structure where the first electrode and the second electrode are mutually engaged with a gap of a constant width between the mutual comb tooth portions.
In the piezoelectric/electrostrictive device of the present invention, preferably, the movable portion, thin plate, and fixed portion are made of an integrally formed ceramic, and more preferably, the movable portion, thin plate, and fixed portion are made of completely stabilized zirconia or partially stabilized zirconia, and particularly preferably, at least the movable portion, thin plate, and fixed portion are constituted by green sheet layered bodies.
Furthermore, in the piezoelectric/electrostrictive device of the present invention, preferably, the piezoelectric/electrostrictive film constituting a piezoelectric/electrostrictive element is made of a material containing lead zirconate, lead titanite, and lead magnesium niobate as main components, and more preferably, the film is made of a material containing sodium bismuth titanate.
In the present invention, there is further provided a manufacturing method of a piezoelectric/electrostrictive device which has a driving portion including thin plates facing each other and a thin film piezoelectric/electrostrictive element formed on the surface of at least one of the thin plates, and a fixed portion and a movable portion shaped like a rectangular parallelepiped, wherein the thin plates facing each other are spanned so that sides of the movable portion and the fixed portion may be continuous, in which said manufacturing method comprises the steps of: obtaining a unitary layered body by laminating at least one green sheet to be the thin plates, at least one green sheet where at least one hole portion having a rectangular-like shape is formed, and further at least one green sheet to be the thin plates; forming a piezoelectric/electrostrictive element on the surface of the green sheet to be a thin plate by a thick film method or a thin film method; and cutting the layered body in the laminating direction of the green sheets so that the above hole portion having a rectangular-like shape may be open on the side of the layered body after sintering the layered body.
In the present invention, there is further provided a light shutter for controlling penetration and shielding of light by relatively displacing two shielding plates, comprising:
a piezoelectric/electrostrictive device which comprises:
a driving portion driven by displacement of a piezoelectric/electrostrictive element;
a movable portion operating on the basis of a drive of the driving portion; and
a fixed portion for supporting said driving portion and movable portion, and in which the device has a driving portion including thin plates facing each other and a thin film piezoelectric/electrostrictive element formed on a surface of at least one of the thin plates and said fixed portion and said movable portion are connected by the driving portion,
wherein at least one shielding plate is attached to the movable portion of the piezoelectric/electrostrictive device.